You've come to the realization that you're trans and you might be thinking, "What do I do now?" The road to becoming your true self can have a few pot holes and nice roadside stops where you can enjoy a hot fudge sundae, but it's seldom boring! Some describe it as a rollercoaster ride and I agree!
How well you transition can be based on many factors. Such as where you live, age, trans resources in your area, how your family and friends accept you, being married or in a relationship and the potential for transitioning at a job. There are some basic steps most of us have taken.
Finding a gender identity therapist can be easy to impossible depending on where you live. Most large cities have them. Some alternative and gay & lesbian publications have listings of therapists, or check the yellow pages under "gay & lesbian." Networking with other trans people will often get you leads to therapists in your area. If you have several therapists to choose from pick the one you feel most comfortable with.
Like many things in transition, therapy can be expensive. Try to have your therapy, and hormones, covered by insurance. You can sometimes have your therapy covered, even if your insurance has exclusions for gender identity, if your therapist uses "anxiety" or "adjustment disorder" as a diagnosis. Likewise hormones may be covered if your doctor uses hormone imbalance as a diagnosis. If you have to pay out-of-pocket some therapists charge on a sliding scale (cost is proportional to your income).
Most surgeons require 6 months of gender identity therapy before SRS. Avoid going to a therapist or doctor who doesn't have gender identity experience. Though you can sometimes educate an unknowledgable therapist, or doctor, it's best to avoid them. They sometimes do more harm than good by misdiagnosing you, not knowing how to prescribe medications, etc.
A support group is a safe place to meet for support and camaraderie and make new friends. If you're in, or close to, a major city there are probably one, or more, trans support groups. They may be harder to find in small towns and less liberal areas. Alternative and gay & lesbian publications can have listings of support groups. You can sometimes get info about support groups from a GLBT-friendly doctor or therapist, or your trans friends. Avoid going to an exclusively crossdresser group, their issues are different than ours. If there are no support groups in your area you might consider starting one.
This ties into the preceding support groups. Transition can sometimes be difficult and lonely. Having a network of supportive friends and allies is important, especially if you're currently in a relationship and your partner is unaccepting, or you're having family problems. Women are generally more accepting and easier to approach. Finding a GG (genetic girl) who befriends, and helps, you is a gem!
Of course, if your current friends accept the new you they become your support network. You'll find out who your real friends are by coming out! Trans-friendly bars or night clubs are another source for finding supportive friends, but be careful as some people's motives may not be as they appear. There are online TS / TG support groups and communities and they can be a great source for internet friends and networking, especially if you're in an isolated or transphobic area. To find one I recommend typing "online trans support group" into google.
Since we've lived some, or most, of our lives as the wrong gender we usually need to unlearn the traits we developed growing up. This comes naturally to some, others have to learn it. A good way is to study female's (or male's if you're FTM) mannerisms and imitate them until they come naturally. Either vocal surgery, or voice training, is usually necessary (except FTMs, their voices become deeper with testosterone).
Most marriages don't last through transition. That is an unfortunate, but common, consequence of transitioning. A few doit helps if your partner is bi or has lesbian tendencies. I recommend giving your partner accurate information about GID, i.e. it's a biological condition and not a choice. People have misunderstandings about us, may think we're being selfish and "destroying the family" without any regard for them. In addition, we can be saddled with guilt and your spouse, or partner, may compound that by trying to make it "your fault." Couples counseling with a gender therapist may help, but most marriages end in separation and divorce. Sometimes a partner may be supportive, or neutral, at first, but as the physical changes become more pronounced and the reality sets in he or she may become unaccepting, even hostile.